Hearsay...ya gotta wonder where people get their info sometimes and then why they repeat it.
Yes, you can hang things from engineered trusses. The answer is always, how much??
Do you have sheet rock on the ceiling now? To give you an idea of what a system can hold, typical ceiling rock is over 2 pounds a sq ft (2.2 more likely). Add mud, lights, door openers, and truss planking, and you're over 1000#'s for a small garage, just hanging on the bottom side. Most codes allow up to three layers of shingles (ugh...bad plan, but another day). Add 4#'s per sq ft, per layer for that. Three layers on that small garage with avg slope, would add another 6600#'s.
Dependent on where you are, you'll probably have snow loads as part of the equation too; 10, 20, or more pounds, per sq ft factored in.
Throw in a guy working up there for a spot load (working in the attic).
Can you hang a canopy? Two options for you here: hire a licensed engineer and have him run the numbers and give you a piece of paper saying yah or nay (I like engineers by the way; I am just fully incapable of performing that job) or throw a hat into the realm of common sense based on readily available data. Latter works pretty good for that minor stuff.
Full disclosure; I'm not an engineer (redundant statement now), but I've installed at least one truss, can read drawings, code, and building requirements, can add sometimes and have been in the industry for over 30 years. And I stayed in a Holiday Inn Express once.
